Have you considered this is due to the overarching change in the startup society as a whole? I mean, have you HAD an actual conversation with other startup founders/CEOs/early employees lately? :) Either they have nothing to say (because they're so new to the scene and probably have an IQ of around 100), or they are ubercritical (because they've seen SO many microcompanies come and go and they're still around - so everyone wants their advice).
Don't take it personally - their meaning isn't what's changed, it's their wording. Saying "I hate your UI" is essentially the same as saying, "Your UI needs to be cleaner." Look at extremely negative comments as a way to start an excellent conversation:
Them: "I hate your UI."
You: "I know! I wish it was cleaner. What do you think about this toolbar?"
If someone is willing to give you honest "I hate" or "I love" feedback, they're ASKING you to want their opinion. And it sounds like you do - so ask them something in return.
And read if you haven't already: http://www.launch.co/blog/good-to-great-to-excellent-a-roadm...